A technique that uses an inkjet print head to preform printing is known for printing identification information such as characters, letters, marks or the like on a tablet. In the tablet printing apparatus using this technique, tablets are conveyed by a tablet conveying device such as a conveyor. Ink (for example, edible ink) is ejected from a nozzle of the inkjet print head located above the tablet conveying device toward each tablet passing under the print head to print identification information on the tablet. As a tablet conveying device, a device that sucks and holds tablets on a conveyor belt has been developed. A plurality of suction holes of, for example, circular or rectangular shape are arranged so as to line up in the conveying direction of the tablets in the conveyor belt of the suction type tablet conveying device to suck and hold the tablets.
In the conveyor belt of the suction type tablet conveying device, tablets supplied onto the suction holes are held on the conveyor belt by suction from the suction holes. However, there are cases where the suction hole is not completely closed by the tablet. That is, a portion of the suction hole may not be closed depending on the size, shape, posture, or the like of the tablet. Besides, the suction hole may not be closed at all due to random supply of the tablet. When the suction hole is not completely closed by the tablet, an airflow is generated above the suction hole as the air is sucked from the suction hole. When the tablet is being conveyed, the surface of the conveyor belt moves along the conveying direction of the tablet. As a result, an airflow flowing along the conveying direction of the tablet also occurs on the conveyor belt due to the movement of the conveyor belt. Such various airflows are mixed and generate turbulence. Further, when the print head and its surrounding members are located above the conveyor belt, the airflow flowing above the conveyor belt strikes these members, which generates further turbulence.
When an airflow such as the turbulence occurs below the print head or in the vicinity thereof, powder of the tablet adhering to the conveyor belt or the tablet may fly and adhere to the nozzle surface (the surface on which the nozzle is formed) of the print head. If the tablet powder adheres to the nozzle surface, the nozzle may be clogged, resulting in ejection failure, or the ink ejected from the nozzle may not fly normally and land at a position other than a desired position on the tablet, resulting in reduced print quality.
In addition, if an airflow such as the turbulence occurs below the print head or in the vicinity thereof, when the tablet passes under the print head, the tablet sucked and held by the conveyor belt shake due to the turbulence and the posture of the print surface of the tablet cannot be maintained. If the posture of the print surface of the tablet cannot be maintained, the ink may land at a position other than a desired position on the tablet, resulting in reduced print quality.